# EPUBCheck PKG-005: extra field on mimetype, how to fix it

Source: https://epubcc.com/epubcheck/pkg-005/ (updated 2026-11-04)

EPUBCheck PKG-005 is an error message: “The mimetype file has an extra field of length …. The use of the extra field feature of the ZIP format is not permitted for the mimetype file.” The mimetype entry in the ZIP carries an extra field, which the EPUB container rules forbid for that one file. Reading apps identify an EPUB by finding the mimetype text at a fixed position near the start of the file, and an extra field moves it.

- Official message (EPUBCheck 5.4.0): The mimetype file has an extra field of length %1$s. The use of the extra field feature of the ZIP format is not permitted for the mimetype file.
- Default severity: Error

## Typical causes

- ZIP tools that add extended timestamps or file attributes to every entry by default, as many desktop compressors do.
- Re-zipping the book folder with the operating system's built-in compress command.

## How to fix it

1. Do not edit the archive in place: rebuild it from the book folder.
2. Zip the mimetype file without extra attributes. With Info-ZIP the -X option leaves them out: Rebuild the archive with the mimetype file first and stored uncompressed, for example from the folder that contains the book: zip -X0 book.epub mimetype and then zip -rX9 book.epub META-INF OEBPS (use your own folder names).
3. Validate again to confirm the message is gone.

## When it's not this

If mimetype is missing or not first, that is PKG-006; if its text is wrong, PKG-007.

## Sources

- EPUB 3.3, §4.3.3 OCF ZIP container media type identification: https://www.w3.org/TR/epub-33/#sec-zip-container-mime (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.